Pretreatment of iron containing base plates and their use in photoengraving



United States Patent 0 3,189,459 PRETREA'IMENT 0F IRGN CONTAINING BASEPLATES AND THEIR USE IN PHDTO- ENGRAVING Michael Kocsuta, 327 E. 285thSt., Willoughby, Ohio No Drawing. Filed Apr. 4, 1960, Ser. No. 19,484 19Claims. (Cl. 96-36) This invention relates to a process for themanufacture of offset printing plates, engraved plates, embossing andstamping dies, etc. It also relates to an improved process involvingpretreatment of plates which permits the use of steel plates for suchpurposes. It further relates to an improved method of applying aprotective coating to metals. This is a continuation-in-part ofapplication Serial No. 710,394, filed January 22, 1958, now abandoned.

For various reasons, the printing industry has used zinc, aluminum,magnesium, or copper plates for the manufacture of offset printing andother types of printing plates. Plates of these metals havedisadvantages in that they are much less economical and more brittle orweaker than steel plates. However, although there have been variousmethods proposed for the manufacture and use of steel plates for thesepurposes they have not been used satisfactorily and the printingindustry has continued to use zinc, aluminum, magnesium, or copper. Ithas even been proposed that a bimetallic plate be used having a base ofmagnesium and a skin of zinc in order to gain advantages of theproperties of both metals. One reason for the reluctance toward usingsteel or any alloy containing a substantial amount of iron is the factthat the resist or protective coating does not adhere as Well to suchmaterials. The term or noun resist as used herein is intended to mean amaterial which when coated on a metal surface will protect against (orresist) the action of reagents which would otherwise attack the metal.

Generally the steps of preparing a printing plate are as follows:

(1) The plate is grained to provide a rough surface to give improvedadhesion of the image-receptive substance to be placed thereon and alsoto give better water-retaining or grease-resistant surfaces in the caseof wet offset printing. Graining is a highly specialized skill and mustbe done properly to assure effective results.

(2) The plate is then coated with a resist which is a light-sensitivematerial such as ammonium dichromate mixed with albumen, glue, gum, orgelatin, etc.

(3) This coating is dried. The coating and drying are carried outsometimes by placing the plate on a whirler.

(4) After the coating has dried, the image or design which is to bereproduced on the plate is laid over this coating. This image may be inthe form of a negative or positive which allows light to shine througheither in those areas representing the image, or in the nonimage areas.Upon exposure, this light activates the ammonium dichromate, or othersubstance performing a similar function, so that it acts to harden thealbumen, glue, gum, or gelatin, etc., in those areas which it strikes.In those areas not receiving light, the albumen, etc., is not hardened.V

(5) The plate is then developed by covering with a liquid whichdissolves, removes, or washes away the unhardened albumen or othercoating material. Thus, if the light was transmitted in the image areas,the hardened areas result in a raised surface which, upon theapplication of ink, will print the desired image or design.

When the metal in the unprotected areas is to be etched away orrecessed, the lateral edges of the hardened coat ing are very oftenprotected by the application and melt- 3,189,456 Patented June 15, 1965ICC ing thereon of a powder substance known as dragons blood, which is ared pitch taken from East Indian trees, and a solution is applied to thenon-protected metal areas to eat away the metal for as long as thedragons blood can protect the hardened coating and metal thereunder.

In the process known as the deep etching process," the above techniqueis varied in that the coating in the printing areas of those areascarrying the image is not hardened. Then the soft areas are washed offso as to leave a stencil of the print or desired image. A deep etchsolution, generally hydrochloric acid in anhydrous alcohol or glycerine,is thereafter applied to the exposed metal to give an indentation ofabout 0.00l-0.002 inch. This recessed area is then filled with gumarabic, or other material which can be hardened. After the gum arabic ishardened, the hardened albumen areas are removed so that the gum arabicareas give the raised printing or image area.

In present commercial practice high humidity has a very damaging effecton the rate and type of drying of resist coatings. The adhesion andquality of the resist can be so adversely affected by humidity that itis sometimes necessary to avoid application of the resist during periodsof high humidity unless humidity control equipment is used.

As can be seen from the above description, the manufacture of printingplates is a complicated process involving very careful control at thevarious steps, particularly where the image or print is to be reproducedin very fine detail. 7

As indicated above, printing plates made from zinc, aluminum, magnesium,or copper have various disadvantages. For example, zinc plates arerelatively soft and somewhat brittle and are therefore subject to wearand fracture under the heavy abuse they receive on painting presses.Magnesium is more expensive, re-. quires the application of specialimaging materials which have to be baked on, and is also somewhatbrittle. Moreover, the coating or imaging material is softer than themetal and sometimes chips off during printing operations, especially ifa large number of copies are being made.

In preparing engraved plates or intaglio plates, either by mechanicallygouging, or by pantograph cutting, or by etching, there have been verydefinite limitations on the accuracy and fidelity of reproducing thedesired image. In the case of mechanical gouging, or cutting, this isdue to human inability to produce very fine detail by laborious methods.With regard to etching, the inaccuracy in detail is caused by the factthat the resist or protective coating is so poorly adhered to the metal,or is so soft in the region in contact with the metal that, as thesolution eats into the metal, it also creeps under the resist orprotective coating layer so that the unetched areas in the metal are notan exact reproduction of the image or print areas desired.

Very often dies which are to be used to stamp or emboss an image ordesign in plastic, metals, etc., need to be hardened in order to standthe abuse encountered during the stamping or pressing operation.Generally this hardening operation is performed after the die has beenformed with the image to be reproduced. In such cases, the hardeningoperation, which involves treatment at high temperatures, results indeformation, alteration, or warping of the image surface so that thedimensions of the ultimate product are not a faithful reproduction ofthe desired image or design.

Moreover, in the production of printed, stamped, or embossed productsdepending on reproduction of a design or image pressed thereon, the rateof producing such articles can be increased tremendously if suchimpression is received from a roll or cylinder on which'the design isimprinted so that the pressing operation is a continuous, uninterruptedone. However, such speedy operation is not always practical in view ofthe 'fact 7 a that the reproduction of a design or image on a'roller orcylindrical form cannot always be done economically or accurately.

One purpose of this invention is to permit the use of e inexpensivesteel for the manufacture of printing plates, engraving plates,embossing plates, dies for lIljfJCilOll molding machines, dies formanufacturing printed ci rcuits,etc. Y 7 j.

. Another purpose of this invention is to'provide a pretreatment ofthesteel which results in improved adhesion of the resist or protectivecoating materials. 7 v

Another purpose of this invention is to, provide a method of applying aresist or protective coating to steel that gives 'a more durable coatingunafiected by high humidity conditions;

. Another purpose of this invention is to give 'a type of etching suchthat the printing areas are of the metal itself-so that acoating is notrequired on the printing areas .to retain ink. a

' a Another purpose of this invention'is to give a process ofetchingthat can be usedto reproduce images easily and accurately oncylindersor rolls. a

Still another purpose of this invention is to provide a 7 process whichcan give accurate and faithful reproduction of images even when theetching is carried to depths much greater than previously used,therehy'perrnitting the use V a d a to 140 F., allowing the compositionto this temperature range is appropriate for mosttypes of resists, it isparticularly appropriate for the dichromate type ofphoto-sensitiveresists. 1 a

When a light-sensitive coating or photo-resist is used,

' an image is exposed on the coating, for example, by placof thisprocess for manufacture of embossing. rolls, dies for producing printedcircuits, dies or molds for injection molding machines, etc. a

' .Still another purpose i s to provide an etching process which canbeapplied to steels prehardened to any degree e of hardness before theimage 'is etched thereon, and 7 thereby give an accurate, economicalreproduction ofthe Z desired image or designin extremely hard metal.

These purposes and others which will become obvious accomplished bythepra'ctice of the present invention.

' uponreading of the invention described herein can' be Ithas been foundthat steel platescan be used, in accordahce .with thepresent invention,to reproduce images thereon useful for printing, stamping, molding, etc.The 'first step involves a pretreatment of the metal with an aqueoushydrochloric acid solution containing about 30- 5 3Lgrams of hydrogenchloride per gallon of solution,

preferably .44- grams, at an elevated temperature of Etc 140 F.,preferably- F. to P. (such solutions can he made by .using 2. 5,to.4fluid ounces, preferably 3.5-4 ounces, of concentrated hydrochloric acid'(36 to 38 percentvby weight) per gallon of solution.)

Sutficient solution is added torwet theentire plate, and

I the solution is left in contact withthe plate for about 2 to .6minutes, depending on the exact acid concentration,

the exact temperature used, and the type of metal used. ;For example,when the preferred rangeof acidconcen tration and the preferred range oftemperature are used, a

the period is advantageously about 4 minutes, for metals containingiron- L Then the solation is washed oiffthe plate with water in such amanner asnot to lower substantially the temperature of the plate, foriexample 'by using water warmed to approximatelyfthe same temperaturc asthat ofthe plate. Regardless of the type of resist or coatingsubsequently-appliedto the steel pla te, it is herence of the resistorcoating.

V. The'subsequent steps in thepreparatrdn of the plate can vary,depending on the type ofplate being used, the type of resist being used,and the ultimate purpose for steps comprise coating the platewithaprotective material ,orresist while the plate is maintained at atempera *ture in the range of 110 F. to 140 F., preferably 120 F.

' found that this pretreatment'irnproyed receptivity and ading over thecoated area of the plate an image-bearing sheetwhich willpermitithe'transmission of light in cer-, tain areas and thereby permitlight. to act on the coated composition in thoseiareas so that the imagecan'be reproduced either as'a positive or 'negativein the coatcdcomposition on the plate; then the composition is developed toremove thecoating in the 'unhardened areas.

Finally, theuncovered areas of the plate are etched to a desireddepth. ei

It has been found also that the method of applying and drying the resistor protective coating on the plate while the plate 'is maintained attheabove temperatures, gives improved adhesion and'improvcd quality ofresistor protective coating even when steels are usedcontainingsubstantial proportions of metal other than iron, such as thevarious stainless steels. This technique also can; be

used to make tougher coatings'of improvedadhesion' and thereby moreaccurate plates from' various steels including the high and lowcarbonsteels, the varioussteels containing hardening materials, such asmolybdenum, tungsten,-etc., and the Various stainlessfsteel-scontainingsubstantial proportions of chromium or nickel, or both, etc;These include the plaincarbon steels, low alloy steels,

corrosion and heat-resistant iron alloy-s, and the stainless andheat-resistant steels listed on pages 864-866 oflanges Handbook ofChemistry, ninth edition, 1956; Included also are the high strengthcastings containing substan 'tially. no impurities or alloying metals.

known, carbon steels have .very little metal present other As isgenerally than theiron. The'other metals are sometimes, present merelyas. traces ofimpurities. Generally, j the carbon content isindicated inthe designationof the carbonsteel. 1 For example,.10='l0 carbon steelindi cates a carboncontent of 0.10 percent. 7 The diliiculty ofobtaininggood steelsis well known. However, by the-lpractice of thepresent invention, excellent adhesion even on such-steels Iisobtained-andthe finished producthas lost substan tially' noneoftheoriginal lustre of the stainlessst'eel.

One of the chief advantages of this invention'isthat this process allowsaccuratereproduction of design in the i cheapest type of steels, such asthe-type commonly re ferred. to .astin plateand carbon steels. Moreover,the

process of this invention also lends itself to quick and accuratereproduction in engravers steel and: also in prehardened. steels. It ispossible by the practice} of this invention to'engrave accurately inthehardestisteel a design which subsequently can be pressed ,in a numberof pieces of other metals, such as copper-beryllium alloy,

which will be usedin turn as moldsforplastics, .etc.

While .it' is not intended thatthisinvention be restricted to any suchtheory, it is believed that the raised temperatureof the rrietal surfacecauses the resist or protective coating to hardenfrorn the metalsurfaceiout wardly throughthe thickness of resist or coating, whereastne.v regular system of drying the resist or protective coating layerwiththe metal at ordinary, temperatures results in having the outersurface of the resist harden'or; dry

first andthe inner or metal-contacting surface. dry last, i

and possibly'n'ot as well as the outer surface, ,Very likely this lattersystem leaves the inner surfaceof the resist v softer and more poorlyadhered to the metal surface ywhich the plate is to be'used. .However,the essential V In accordance with the practice 'of thi's' in vention',it

.is generally preferred, in. the manufacture o f p'rintingi' plateshaving raised printing areas, to have the etched.

area recessed sufiiciently so that the coating roverqthe unetched orprinting areas can be removed and the raised areas of the. unetchedmetal 'itselfrserve' as the printing v dry, and then allowing the plateto cool at room temperature. While adhesion to stainless" areas. In thisway the metal, being much stronger than the composition with which itwas coated, is less subiect to chipping and cracking during abusiveprinting operations. Apparently because of improved adhesion of theresist or protective coating, the process of this invention permitsdeeper etching and more accurate reproduction of print, image, or designthan has previously been known. Since this can now be done in steel, theprinting and image surfaces are harder and less susceptible tomechanical abuse, and can be produced more economically.

The pretreatment step described above leaves the printing area receptiveto inks and excellent results are obtained by using the plate in thismanner. Moreover, since harder and tougher metals such as steel can beused, a greater number of copies can be printed without concern overvariations or changes in the actual printing. Furthermore, since theplate can be used without fountain solution, this permits the plate tobe used for extended periods without periodically having to examine theprinted sheets to determine whether scumming or intermingling of thewater and ink has occurred on the non-printing areas of the plate, whichnecessitates removal and treatment or replacement of the plate.

Even where it may be desirable to prepare and use the plate in the samemanner as presently used with wet offset zinc plates, for example, whenonly a few copies are to be printed, the present invention offers anadvantage in that it permits the use of more economical steel plates andgives improved adhesion of the coating material or resist.

The invention is best illustrated by the following examples. Theseexamples are not intended to serve as limitations on the scope of theinvention described herein but are intended as illustrations of variousmethods in which the invention may be practiced. Unless specificallyindicated otherwise, references to parts and percentages are intended tobe parts by weight and percentages by weight.

Example I A thin sheet of 1020 cold-rolled steel 0.015 inch thick, 9inches Wide, and 20 inches long, is placed on a heated steel plate inchthickness and having sufiicient area to support the entire sheet. Thisheater plate has heater elements underneath, thermocouple for indicatingtemperature thereof, controls for adjusting the temperature, andadvantageously is placed in an area having good ventilation. The thinsheet is heated in such a manner that the temperature throughout isrelatively uniform and not over or under-heated in any area. Means formeasuring the temperature of the sheet are attached or placed thereon.With the temperature of the sheet maintained at about 125 F., the entirearea of the sheet is treated with aqueous hydrochloric acid solutioncontaining 4 fluid ounces of concentrated hydrochloric acid (36% byweight) per gallon of solution. The solution is of such a temperaturethat its contact with the sheet does not lower the temperature thereofand the sheet is maintained at about 125 F. The acid solution is left incontact with the sheet for about 4 minutes, after which the solution iswashed oif with Water having a temperature of about 125 F.

An albumen photo-resist solution (prepared according to the proceduredescribed at the end of this example) is applied to the plate while thetemperature is maintained at about 125 F. This resist is sprayed on tothe plate to give a thin, continuous, uniform coating thereon. After acoating of relatively uniform thickness has been applied, the coating isallowed to dry. The drying is completed within a matter of minutes. Theplate is then removed from the heater plate and placed in an areaprotected against actinic light until the plate has reached roomtemperature. The remaining surfaces of the plate,

including the sides and back, are coated with a considerable thicknessof asphaltum and dried. A photographic negative bearing the imagedesired for reproduction is placed on the plate and the plate thenplaced in a vacuum frame for exposure. The negative with plateunderneath is then exposed to actinic light from a 20 ampere carbon arclamp for six minutes. The plate is then taken out of the vacuum frameand developed with a calcium chloride developer, (made by adding 53 ml.of lactic acid to a liter of 4041 Baum aqueous calcium chloridesolution) until a clear image is obtained; the plate is next Washed withalcohol and dried. Then the plate is dipped into a tank of mordantcomprising 41 Baum ferric chloride solution agitated at 80 F, for aperiod of about one hour. Thereafter the plate is removed from themordant bath and washed with water to remove the resist layer. The platehas the image reproduced thereon with printing surfaces raised about0.0060.010 inch above the recessed areas.

The plate is placed on a dry, offset printing press andv after 5,000,000copies of printed material are run off, the plate shows no signs of wearand final copies of the printed material are as good as the firstcopies.

The following procedure is used in preparing the albu men photo-resistsolution which is used in above pro cedure. Egg albumen crystals (4 /2avoirdupois ounces) are placed in a cheesecloth bag and suspended in 22ounces of water until dissolved. The bag is then removed withoutsqueezing. A volume of this solution is measured out which contains 3avoirdupois ounces of albumen. This can be checked by determining thedensity of the solution and referring to the density chart on page 49 ofthe book entitled Photography and Plate Making for Photolithography, byI. H. Sayre, published in 1939 by Lithographic Textbook PublishingCompany, Chicago, Illinois. To the quantity of albumen solutioncontaining 3 ounces of albumen, are added 5 liquid ounces of dicchromatesolution made as follows: 16 avoirdupois ounces of ammonium dichromateare dissolved in 64 fluid ounces of water, the solution is filtered, andWater is added slowly until a hydrometer reading indicates that thesolution has reached a density of 142 Baum. A small amount of RhodulineBlue dye is added to give color contrast upon development of the plate.

Example II The procedure of Example I is repeated except that aphoto-resist solution is used which is prepared as follows: 60 grams ofpurified, dewaxed shellac are heated with 75 ml. of aqueous ammoniasolution (28% ammonia) and 250 ml. of water until dissolved. Then 70 m1.of 3% aqueous ammonium dichromate solution is added and the solutiondiluted with 100 ml. of ethyl alcohol. A small amount of Malachite Greendye is add ed to give color contrast upon development of the plate.After the exposure step, the plate coating is developed until the imageis clearly detailed, by the use of a solution of anhydrous ethyl alcoholcontaining 15 grams of castor oil and 35 mi. of glacial acetic acid.

After treatment with mordant and washing otf of the hardened resist asin Example I, the plate has raised lettering of about .006-0010 inch.This plate is placed on a dry offset printing press and after 5,000,000copies of printed material are run off, examination of the plate showsno signs of wear and final copies of the printed material are as good asthe first copies.

Example III The procedure of Example I is repeated using a plate of 1030steel, inch thick, 9 inches Wide, and 20 inches long. After the platehas been removed from the mordant bath and washed with water to removethe resist layer, the plate is placed on a direct printing press. After5,000,000 copies of printed material are run ofl, examination of theplate shows no signs of wear and the final copies of the printedmaterial are as good as the firs copies.

' definitely.

fir st and the last scufi j V V Exctm'pl e Vl V A roll of 1020 steel 60inches long and. having" an cut 7 Eramplc 1V V A /2 inch thick plate ofengravers steel, 4 inches wide,

-and 6 inches long, 'is used in accordance with the procedure of ExampleII, except that a positiveis used for the'actinic light exposure and theprinting area is etched away to a depth'of 0.004 to 0.006 inch,'byleaving the plate. in the mordant bath at about 60 F. for about thirtyminutes. After the plate has been washed to re: ,;move the resist layer,it is given a hard chrome plating and the plate is used in a graphicarts die'stamping press.

After 50,000 copies of the greeting cards are printed therefrom, somewear of the chrome isevident, apparently as the result of the abrasionof the wiping paper. The

' chrome layer is removed from the plate by stripping, and the plate isgiven another hard chromejplating. Another 50,000 .copies are printedbefore wearing is again apparent. This stripping and plating can berepeated in-' Example V 1 Q Embossing cylinders or rolls are preparedaccording to the procedure'of EXamplelL'nsing two cylinders of 1040 ingan outer cylinder shape slightly less in diameter than 'the insidediameter of the'cylinder to be treated; With one of the rolls a negativebearing the desired design is wrapped aroundthe cylinder and givenactinic light exposu're simultaneously from all sides. The otherroll issimilarly wrapped with'a transparent positive bearing the identicaldesign as in the first case.

Thus, the first roll aftercompletion bears on it a male die and thesecond roll has a female'die of corresponding design.

in such contact that the male design 'on the first roll correprocedureof Luv cording to million pieces molded therefrom which bear thereon anaccurate reproduction of the desired printing and design;

This procedure is repeated on a mold having a cylindrical surface whichis to carry the desired printing and."

design. Similar satisfactory results are obtained in this case.

' Example 1X .The procedure of Example IIis used for the production of a'die to'be used in the manufacture of printed circuits.

The negative used in this case bears the image of a Wiring circuit whichisdesired for reproduction in copper in the ultimate assembled printedcircuit.;-'l"he die is used "in making printed circuits by three wellknown procedures. First, it is used .toernboss and imprint the desiredcircuit by pressing the areas to be retained into i a plastic backingand then grinding off the copperareas which are not to be retained. Inthe secondprocedure, v

the printed circuit areas on the plate were coated with a resistmaterial which was then printed onto a sheet of copper foil laid on aplastic backing. After the resist had hardened, the unprotected areas ofthe copper, were etched away andvt'ne resist layer thereafter washed'offthe protected copper areas which comprise the printed.

circuit. imprint powder powder In the third procedure; the plate wasused to the desired circuit ina thin layer of'copper contained on aplastic backing, the unpressed Example X The procedure of Example IV isused to make 'a master for pantograph engraving. By following therecessed areas of the master, the masjte'r is used satisfactorily forThe two 7 cylinders are mounted on a machine bearing driving rollers 7operating in such a manner that'the cylinders are rotated sponds to andfits into the female design on the second I roll. Thin aluminum sheetingis fed between the two 7 cylinders and the cylinders rotated underpressure so as to emboss onto the aluminum sheeting the design that hasbeen etched into the cylindrical surface. After 2,000,000

automobile scufi; plates havebeen rolled with this design,-

there is no noticeable wear on the cylinder surfaces. 1 Moreover, thereis no perceptible difference between the plates which are so rolled.

side diameterof lO inches, is processedaccordingto "Example V using anegative bearing'a design which is to be imprinted into plasticsheeting.

The desired temperature is obtainedby placing the roll in any oven atthat temperature for half an hour; The roll'has sufficient heatcapacity-to maintain the desired temperature "through the pretreatmentand coating steps.

Thecompletedroll is chrome plated and used to em- .boss thedesign'thereon into plastic sheeting by running the plastic sheetingbetween this roll and a second roll having no design thereon butbeing-rolled in pressure contact with the first roll.

Example VIII I v A platelis made accordingto the procedure of Example111 bearing a design thereon similar to' leather graining. This is usedto imprint grain on synthetic leather.

'Example' VIII 1 One-half of a mold to be used in an injection molding Vmachine'having a number of fiat surfaces in which printing and adesignfare'to be reproduced,is processed acmaking pantograph engravingsV, of larger, smaller, and identical sizeas the design on the master.

Example XI The procedure of Example I is repeated using in place of thealbumen photo resist solution, a gurnja-rabic-arn .monium dichromatephoto-resist solution made as fo llows: 720 cc. clear gum arabicsolution of 14 Baum is mixed thoroughly with: 240 cc. ammoniumdichromate aqeu ous solution containing 17 percent by weight ammoniumd1chromate,=then 36 cc. of an ammonium hydroxide aqueous solutioncontaining 28 percent by Weight of ammoniais added and the mixture isstirred carefully' 7 so as nothto beat air into the solution; theresultantmixe A ture IS strained through 6 or '8 thicknesses -of dam'pcheesecloth. e V

The developer used is made by the following pro-' 'cedure: 350 grams ofzinc chloride is addedto one litre of water; when this isdissolved, 700grams of commercial calcium chloride1(CaCl -2H O is next dissolved; then160 cc. of percent lactic acid is dissolved therein and Water isaddeduntil the hydrometer reading is 41.4-41.5"

Baum at 78-80? After the developing, mordant j treatment, and removal ofthe resist layer withwaterhas' i been completed, the plate is placed'ona dry oifset printing machine and more than 5,000,000 copies of printed.mater'ialrun off. The' final copies'of thte' printed material' areasgood as the'first, and the plate shows no 'signs of wear. 7

Example XII The procedure of Example I is repeated using in place of the.alburnen photo-resist, an isopropyibenzene solutron of llght-sensitivebitumen, developing the exposed coating. with turp entine, and finallyremoving the hard-Q enedres st with benzol. after theetchingmordantftreatmerit. Upon completion of the plate and testing on aprinting press, similar SQtlSfEI-CtOET/TCSUHS 31'6"Obi3iil6dasinEXampleI. A 7

.Eziainple'll using a negative hearing the desired printing and design.The mold is attached to the injection molding machine and'several V wasthereafter removed, and the impressed powder soldered by well-knownmeans. i

Example XIII The procedure of Example I is repeated through thedeveloping stage, using a thin sheet of steel of the same dimensions asin Example I which has previously been grained, as in the ordinarypractice of preparing zinc plates for Wet offset printing. After thedeveloping stage, the plate is Washed with alcohol and dried. However,instead of treating with mordant, as in Example I, thet plate is used ona wet offset printing machine with the resist areas serving as theprinting areas. After 500,000 copies of printed material have been run05, examination of the plate shows no defects in the priuting surfacesof the plate.

In the practice of this invention, other photo-resist materials can beused and it is not necessary that the photoresist material be one thatis sensitive to actinic light. While actinic light-sensitivephoto-resists are preferred, so that the operator can work in ordinaryartificial light, it is suitable to use other photo-resist compositionsprovided proper precautions are taken to avoid exposure of the plateduring the coating, drying and developing stages to the particular typeof light to which the resist is sensitive. Such photo-resists sensitiveto other types of light, as well as appropriate developers, arecommercially available and are contemplated for the practice of thisinvention.

Moreover, it is also not necessary, except where a photographic processis being used, that a light-sensitive resist or protective coating beused to reproduce the desired design or image on the metal plate. Forexample, plates are satisfactorily produced by drawing a design directlyon the plate while the plate is maintained at the desired temperature asindicated above for drying the resist to a tough, well-adhered coating.When the plate is made of steel or has a substantial amount of irontherein, it is particularly advantageous that it be pretreated asdescribed above. The resist or coating material must necessarily be onewhich is not affected by the etching solution for the period necessaryto etch or eat away the metal to the desired depth and also gives goodprotection to the metal right at the contact edge of the resist and themetal against the etching solution. Likewise, a stencil or screen can beplaced on the heated, metal plate and the resist or coating materialapplied through the open spaces of the stencil so that when the stencilis removed, the desired design is reproduced on the plate to give atough, well-adhered resist, which after etching gives the desired designin the metal plate. Resist matertials which can be used for drawing orstenciling include asphaltum, lacquers, paints, enamels, solutions ofthermoplastic resins, etc. The solvents used in these materialsobviously should have a flash point above the temperature of the plateand should be applied under a hood which will draw off vapors, or whensolvents of low flash point are used, the application should beperformed in an atmosphere of inert gas.

For example, a design is drawn on a steel plate while maintained as inExample I at a temperature of about 125 F. using an isopropylbenzenesolution of asphaltum. The sides, back, and other areas of the platewhich are not to be etched are coated thickly with asphaltum, dried, andthen placed in the mordant and further treated with satisfactory resultsas in Example I.

While it is preferred in the practice of this invention that the resistcoating be applied by spraying, it also is satisfactory to apply suchcoating by various other methods, such as spreading, or allowing thecoating to run over the surface of the plate, or by placing the plate ona Whirler, provided means are available to maintain the temperature ofthe plate within the desired range. The whirler can be equipped 'with aheating element under its surface, or can carry it on a heating elementon which the plate will be placed. It is also possible in cases wherethe plate is of suflicient thickness to maintain the desired temperatureby its own heat capacity, that a whirler can be used which does not haveheating means. However, it is desirable to avoid the use of hot airblown onto the whirler or radiant heat from above to expedite drying, asis generally the practice. It is more desirable, as indicated above,that the heat for drying be supplied from the plate itself so that theresist is better adhered to the plate and is built up to a tougherthickness. Regardless of the method of applying the coating to theplate, it is desirable that a uniform, continuous coating be depositedon the plate. The thickness of the coating is generally in the samerange as is presently applied to zinc and other types of plates. Thethicker the coating, the greater is the time required for exposure toharden the coating, and the thinner it is, the shorter is the timerequired for exposure. However, the coating should not be so thin as torisk bare spots or ,uncoated areas on the metal.

As indicated above, various types of steels can be used in the practiceof this invention, although it is particularly'advantageous with respectto metals containing a substantial amount of iron since it haspreviously been found particularly difficult to obtain good adhesion ofresist and other coating materials with such metals; All types of steelsare included. Steels or steel alloys are considered as containing atleast approximatel ten percent iron. While the process of this'inventionis useful with all of such steels, it is particularly appropriate withalloys containing approximately a major part of iron therein. t

For example, those having very low carbon content, such as 1010 steel,and ranging in carbon content all the way to the very high carbonsteels, such as high grade tool steels, can be used. The hardness of thesteel does not appear to interfere with the practice of this inventionsince steels of 70 Rockwell C hardness are used advantageously.

As previously indicated, stainless steels also have offered particulardifficulties in obtaining good adhesion with resist materials and alsoare advantageously used in the practice of this invention. Such steels.include those containing nickel, molybdenum, tin, chromium, manganese,etc. When high carbon steels are used, it is desirable to brush theetched surface of the steel after it has been in the mordant severalminutes since the carbon deposited on the surface slows down the actionof the mordant. The higher the carbon content in the steel, the soonerand more frequently will the brushing operation be desirable.

It is also desirable that the various metals be in a clean conditionwhen used in the practice of the invention. For example, it is desirableto remove any oxide coating, or rust, or oils from the surfaces of themetal. This can be done advantageously by cleaning the metal with waterand pumice before use.

In addition to the various types of light-sensitive photo-resistsdisclosed above, various other types of photo-resist coatings can beused in the practice of this invention. Generally, with such otherphoto-resist materials, the temperature range indicated above forapplication and drying of said coating also is preferred. In someinstances where such other coatings are applied at temperatures belowthis preferred temperature range the results are erratic, the adhesionof the coating being sometimes satisfactory but in any case the resultsare improved by the acid pretreatment of the metal surface as describedabove as compared'with the metal not so pretreated. However, when thepreferred temperature range is used, the adhesion is excellent in everycase.

Typical examples of such other photo-resist materials that can be usedin the practice of this invention include various light-sensitivepolymers, such as polyvinyl cinnamates, light-sensitive alketonecompositions, light-sensitive vinyl-substituted benzal acetophenones,styrene- Example XIV steel;

' aieacso maleic cinnarnide .copolymers, light-sensitivepolymericquaternary salts,'etc., such'as disclosed in U.S. patents:

1,965,710 I r 2,670,287 1 2,100,063 2,670,286 2,312,852 2,690,966 a2,373,357 2,691,584 2,484,451 2,697,039 .2,500,028 5 2,714,066.

, Ithas'been found that by the practice'oi' 'this inven-- tion excellentresults can be ohtainedusing lessfexpensive dichromate albumen types ofresists' Moreover,

results with the'polyvinyl cinnamate and 'Other types of resists areimprovedlalso. For example, the instructions 'on one ofthe polyvinylcinnamate commercially available compositions recommendbakingthe resistas one of, the final steps to insure adhesion of the resist to themetal, It has been found that excellent adhesion to the metal isobtained with that commercial product without the baking step whenapplied according 'to the process ofithis invention, whereas when thisprocess is not used, this product required the baking step to givesatisfactory adhesion; 7 e

7 The following examples illustrate' theuse of additional resistcompositions. a V I J Example XIV drying' Thejthird plate whichhasreceived only the pumice cleaning treatment is' coated similarlywhilethe plate ismaintained at about 125." i j 1 V 9 After dryin gpeach of'the coated plates is" exposed in accordance with the exposure proceduredescribed above in Example 1. In each case, the exposed plate isdeveloped in accordance with the procedure of Exam ple-l, of theaforesaid patent and is then etched in a 1 mordant comprising 41 Baun1ferric'chloride solution agitated'at 80 F. for aperiod of about onehour. A

comparison of ,the resist coatings on'the respective plates showserratic resultswith the first plate, some areas being satisfactorilyadhered and certain spots not well adhered. Very excellent results areobtained with the secend plate, which has received both the pretreatmentand the resist application and drying at raised temperature.-

The third plate ivhich did not have the acid-pretreatment showedunsatisfactory adhesion of'the resist layer. 'Processing of the secondplate with fer'ric chloride solution and subsequent removalof the resistlayer gives an etched image of fine detail; a.

. V ExampleXV Similar results areobtained when the procedure of.

is re'peated'using plates of'310 stainless Example XVI I The procedurcof ExamplesjXlV and XV are repeated 7 with similar results using thealketone photo-resist come position. of Example 2;of theafor esaid'patent, wherein ethyl cellulose is used in place ofthe polymethyl meth-Lacrylate; 7

Example X VII.

* Two 430 stainless steel plates are acid-pretreated in ac- I cordancewith the procedure of the above Example I and. a third similar stainlesssteel plate merely is cleanedvery 7 lightly with pumice. Under subduedlight, each of the three plates'is given a very thin coating of acomposition prepared according to the example of U.S Patent 2,610,120,and containing 25 grams of polyvinylcinnamate, 25 cc. of chlorobenzene,cc, of'toluenaand 0.25 gram'of 2,4,6-trini-troaniline. a

a The coating is applied .to the first pretreated plate while the plateis at room temperature, to the second pretreated plate while it ismaintained at about 125 F.', and tothe third, or untreated plate,.whileit also is maintained at about 125 F. After drying, each of the platesis exposed under an image negative at fourfeet from a 35-ampere whiteflame carbon arc for aboutoneminute. Then the exposed plate is developedin each case for two minutes in a tray of methylethylketdne. ;While the.resist coating.

on the first plate is erratic, as described in ExampleXlV, that on thesecond plate shows excellent adhesion. The

third plate shows very poor adhesion. I Treatmento'f the second plate ina ferric chloride mordant bath and subse: quent removal of'thehardenedresist results fined images in the stainless steel surface; 7

Example XVIII V 1- Similar. results are obtained when. the procedure ofExample XIV is repeated using as the resist coating thecom position ofthe example in US. Patent 2,670,285, which contains 2.5 grams ofpolyvinyl cinnavmate, cc. of methyl glycol acetate, 0.25 gram of2-keto-'3-methyl'-l,3-

diazabenzanthrone, and usingxmethylethylketone as the developer; V e V VExample XIX Similar results also are obtained wheii the procedure ofExample XIV is repeated using the resist coat-ing com-.

position shown in Example 1 of U.S Patent 2,670,286,

containing 2.5 grams, of polyvinyl cinna-ma-te,v 100 cc.

oi methyl glycol acetate, and 0.25 gram of 1,2-henzan- 1 thraquinone,and using methyl'ethy-l ketone as the de' vcloper.

p ExampIeJXX s Similar results also are obtained when the procedure ofExample XIV. is repeated using thercomposition of the exampleofUSgPa-tent2,670,287,.containing' 2.5

grams of polyvinyl cinnamate, .100 cc. of methylglycol acetate, and 0.25gram of 4,4'-tetramethyldiaminodiphenyl ketone, and using 7 Example XXIH 7 V Similar results also are obtained whenflthe procedure of ExampleXIV is repeated using as the resist coating the'composition shown 'incolumn 4 of U.S. Patent 2,690,966, containing 5 grams of polyvinylc'innamate,

0.25 gram of crystal violet earbinol base, 40 cc; of xylene,- 40.cc.;0ftoluene, :10 ccrof 'n-'buty1 alcohol, and 10cc. of

Similar results false areohtained when the procedure of Example XIV isfollowed 'except'that the resist coating is amethylethyllsetone solutionof a polyvinylacetophem one-anisaldehyde condensation product producedacc'ord ing to Example 3 of Patent 2,716,097

ketone used as the developer. i s

" Example .XXIII' 7 Example is repeated The procedure of withisimilar 7results using as the coating composition 'apyridine solu'-. tion of thelight-sensitivematerial prepared according to Example 1' of'US. Patent2,5-l7,373, comprising the re methyl ethyl kctone as the developer.

inethylethyh action product of styrene-maleic anhydride copolyrner withN-(m-hydroxymethylphenyl)-cinnamides sensitized by2-benzoylmethylene-1-methyl-beta-naphthyl-th azoline, and using pyridineas the developer.

Example XXIV Example XXV The procedure of Example 1 of US. Patent2,760,863 is followed, without the primer coat of that Example, inapplying a light-sensitive coating directly on two 1020 carbon steelplates, the first of which is pretreated as in Example I and ismaintained at about 125 F. during the application and processing steps,and the second plate merely is cleaned with pumice and maintained atroom temperature during the processing. The coating of the describedmixture of 55 parts methylmethacrylate monomer, 25 partspolymethylmethacrylate, 20 parts of monomeric polyethylene glycoldimethacrylate, and one part benzoin are applied and processed inaccordance with the procedure described in Example 1 of the aforesaidpatent. The adhesion of the hardened areas of the pretreated plate isdistinctly superior to that of the hardened areas on the other plate.Similar results are obtained when this procedure is'repeated on 305stainless steel.

Example XXVI The procedure of the above Example I is followed in thepretreating of two 310 stainless steel plates, and a third similarstainless steel plate merely is cleaned with a light rubbing of pumice.Using a silver bromide-gelatin emulsion normally used in the preparationof photographic film as the resist composition, a thin layer is appliedto each of the plates. Under dark red light in each case, the coating isapplied to the first plate at room temperature, and to the second andthird plates at about 125 F. in accordance with the procedure of ExampleI. Then each of :the plates is covered with an image negative andexposed for 7 seconds to a 100-watt incandescent light at 3 feetdistance. Each plate then is developed and the unexposed areas washedaway with hydroquinone solution, and the exposed areas then are fixedwith hypo solution containing sodium sulphite and alum. Aiter dryingeach of the plates is examined. The first and third plates show suchpoor adhesion that they cannot be treated in the mordant. The secondplate showed satisfactory adhesion and upon etching in ferric chloridesolution gave satisfactory detail in the etched design. Although theresults are not as excellent as those with the other resists describedherein, they show improved adhesion eflected by the present invention.Similar results are obtained when the procedure is repeated using 1030carbon steel, and also when repeated with other silver chloride andsilver iodide photographic emulsions respectively.

Example XX VII The pretreating and coating procedure of Example )QCVI isrepeated in applying a resist coating to three stainless steel plates.The resist composition is applied directly to the metal and is a onepercent water solution of the light-sensitive diazo resin preparedaccording to the first complete paragraph at the top of column 7 of US.Patent 2,714,066. After the resist has been applied and dried undersubdued light, each plate is exposed under a negative image to lightfrom a 35-ampere carbon are light at 24 inches for 1.5 minutes. Theexposed plate in each case is processed immediately after the coatinghas dried according to the directions of the second full paragraph ofcolumn 8 of the aforesaid patent. The second plate is the only one ofthe three on which the resist coating has adhered satisfactorily. Thisplate immediately is placed in a mordant bath of ferric chloride and thedesign etched in the metal gives excellent detail. When the foregoingprocedure is repeated using ultraviolet light, fluorescent tube blacklight, and light from a photofiood bulb respectively, in place of thecarbon are light, similar results are obtained.

It is possible by the practice of this invention to etch to depths of0.015 inch or deeper While maintaining accuracy and fidelity of detailsin the image. It has been found that the practice of this inventionpermits such accurate reproduction of image that it is possible toproduce plates from which half-tones can be printed since the sizes ofthe dots used for such purposes are easily controlled.

The term image as used herein is intended in abroad sense to includeprinting, diagrams, drawings, pictures, etc.

With respect to the photo-resist materials being used in the practice ofthis invention, the type of light, the strength and the duration of thelight exposure obviously will all be determined by the type of resistmaterial being used. In view of the tougher resist coating produced bythe practice of this invention, it is generally necessary to useslightly longer exposure than is used with resist applied according toprior practice. For example, where certain resists are used in otherprocesses with an exposure time of 2-4 minutes, an exposure time of 57minutes is desirable when such resists are used according to thisinvention.

Moreover, the type of developer and the type of mordant to be used willbe determined by the type of resist or protective coating. Obviously thedeveloper must be one which will soften and remove the unhardenedcoating while at the same time not damaging or removing the hardenedresist. Manufacturers and suppliers of commercial resist materialsgenerally recommend and supply the developer that should be used withtheir particular resist materials. As indicated above, ferric chloridesolution (3844 Baum, preferably 4042) generally is preferred as themordant for use in the practice of this invention. However, othermordants which will attack the metal also can be used, provided theresist is inactive toward that particular mordant. Other mordants whichcan be used with particular resist materials inactive to the mordant arenitric acid, acetic acid, solutions of hydrogen in alcohol or glycerine,ferric chloride solutions containing minor amounts of hydrogen chloride,etc.

While certain features of this invention have been described in detailwith respect to various embodiments thereof, it will, of course, beapparent that other modifications may be made within the spirit andscope of this invention and it i not intended to limit the invention tothe exact details shown above except insofar as they are defined in thefollowing claims.

The invention claimed is:

1. A process for treating an iron-containing metal for improving thereceptivity of an adhesive organic coating on said metal which comprisesthe steps of treating the surface of said metal by intimate contact withhydrochloric acid solution consisting essentially of about 30- 53 gramsof hydrogen chloride per gallon of solution while said metal ismaintained at a temperature of about F. to 140 F. for a period of about2 to 6 minutes, and removing said solution therefrom.

2. A process of claim 1 in which the acid concentration is about 44-50grams of hydrogen chloride per gallon of solution and the temperaturerange is about F. to F.

3. A process for applying to an iron-containing metal a coating of aresist selected from the clas consisting of dichromate light-sensitiveresists, light-sensitive bitumen,

light-sensitive polyvinyl 'cinnamate, light-sensitive diazof resins,light-sensitive silver salt emulsions, light-sensitive vinylmonomer-polymer mixtures, light-sensitive polyt .rneric quaternaryammoniumsalt resins, and asphaltum,

' comprising-the steps of: (1) pretreating the surface of V said metalfor a period ofaboutQ to 6 minutes withhy- ;drochloric acid solutionconsisting essentially of about. 30-50 grams of hydrogen chloride pergallonof solution while the metal 'is maintained at a temperature ofahout l l0 to 140 'F.; and (2) thereafter applying the coating to themetal while the metal is maintained at a temperature in the range ofabout110 F. to 140 F.

4. A process of claim 3 in which theac'id concentration l is'anout 44-50gramsof hydrogen chloride per gallon of solution.

5. A process of claim 6.3A process ofclaim 3 in'which'the coatingisilightsensitive and the coating is subsequently exposed to the a typeof light to which it is sensitive in'such a manner as to producethe'desired image thereon. 7. A process of claim 3 in whichsaid'resistis a dichromate photo-resist. V V V H '8. A process ofreproducing an image inthe surface of an iron containing metalcomprising the steps: (I) treat- .ing the surface of: the metallwithhydrochloric acid solution consisting essentially of about 30-53grams ofhy- V drogenichlon'cle per gallon of solution while the metal'ismaintained at a temperature of about 110 F. to 140 'F. for a periodof about 2 to 6 minutes} (2) subsequently applying a coating of aphoto-resist material selected from a the class consisting oflight-sensitive 'dichromate resists,

light-sensitive polyvinyl cinnamate, light-sensitive bituo 3' in' whichthe temperature is 7 about'120 F. to 140 F.

snaaaeo not receive light duringexposure; and (6) removing' -the V,

softened coating from the metal in the softened'areas;

men, light-sensitive diazo resins, light-sensitive silver salt tures;and light-sensitive polymeric quaternary ammoni- .um salt resins,while-said metal is maintained at a tem- V perature in therange of about110 F to 140 F; (3) L 7 allowing said coating to dry; (4) exposing saidcoating to light of'the'type to which said photo-resist coating issensit .tivein such a manner that different amounts of light strikingdifierent areas of saidcoating reproduce the desired image thereon; (5),placing in contact with said exposed photo-resist coating a, developerwhich softens andmakes removable that part of thephoto-resistcoatingwhich did emulsions; light-sensitive vinylmonomer-polymer mix- 9. A process of claim 8 in which the exposed metalsurfacesfrom which said'sof-tened coatingf'has been removed are placedin contact with a 'mordant solution which etches said exposed surfaces.

'11}. A' process of claim 8 1n comprises albumen and ammoniumdichromate;

11. A process of claim s' inrwhich saidphoto-resist comprises shellacand ammonium dichr'omate, a

, 12. A process of claim 8 in which'said photo-resist comprises alight-sensitive polyvinyl cinnamate compo-.

.sition. V V 1 1 7 g j 13. A process of" claim 8 in which :saidphot'o-resist' comprises gum-arabic and ammonium dichromat'e.

14 A process of claim 8 in which said exposed metal surfaces from whichsaid softened coating has beenfre aqueous solution moved are placed incontact with" an 'of ferric chloride. 15. A process of claim 14 solutionis 38 44 Baum. V V a V 16. A process of claim 14in which said metal is acarbon steel. j V V r 17. A process of claim 14in which'said-metal is astainless steel.

which said ferric chloride 18. A process of claim 9'in which said metalis aprea hardened, steel.

19. A process of claim 14 gravers steel. t

, 'ReferencesCited by the "Examiner V V UNITED STATES PATENTS i VNORMANG. TORCHI N, Pziimiziry Examiner;

:PHIVLIP E. MANGAN, Examiner. e

which said photo-resist inwhich said metal isien

8. A PROCESS OF REPRODUCING AN IMAGE IN THE SURFACE OF ANIRON-CONTAINING METAL COMPRISING THE STEPS: (1) TREATING THE SURFACE OFTHE METAL WITH HYDROCHLORIC ACID SOLUTION CONSISTING ESSENTIALLY OFABOUT 30-53 GRAMS OF HYDROGEN CHLORIDE PER GALLON OF SOLUTION WHILE THEMETAL IS MAINTAINED AT A TEMPERATURE OF ABOUT 110*F. TO 140* F. FOR APERIOD OF ABOUT 2 TO 6 MINUTES; (2) SUBSEQUENTLY APPLYING A COATING OF APHOTO-RESIST MATERIAL SELECTED FROM THE CLASS CONSISTING OFLIGHT-SENSITIVE DICHROMATE RESISTS, LIGHT-SENSITIVE POLYVINYL CINNAMATE,LIGHT-SENSITIVE BITUMEN, LIGHT-SENSITIVE DIAZO RESINS, LIGHT-SENSITIVESILVER SALT EMULSIONS, LIGHT-SENSITIVE VINYL MONOMER-POLYMER MIXTURES,AND LIGHT-SENSITIVE POLYMERIC QUATERNARY AMMONIUM SALT RESINS, WHILESAID METAL IS MAINTAINED AT A TEMPERATURE IN THE RANGE OF ABOUT 110*F.TO 140*F.; (3) ALLOWING SAID COATING TO DRY; (4) EXPOSIG SAID COATING TOLIGHT OF THE TYPE TO WHICH SAID PHOTO-RESIST COATING IS SENSITIVE INSUCH A MANNER THAT DIFFERENT AMOUNTS OF LIGHT STRIKING DIFFERENT AREASOF SAID COATING REPRODUCE THE DESIRED IMAGE THEREON; (5) PLACING INCONTACT WITH SAID EXPOSED PHOTO-RESIST COATING A DEVELOPER WHICH SOFTENSAND MAKES REMOVABLE THAT PART OF THE PHOTO-RESIST COATING WHICH DID NOTRECEIVE LIGHT DURING EXPOSURE; AND (6) REMOVING THE SOFTENED COATINGFROM THE METAL IN THE SOFTENED AREAS.
 9. A PROCESS OF CLAIM 8 IN WHICHTHE EXPOSED METAL SURFACES FROM WHICH SAID SOFTENED COATING HAS BEENREMOVED ARE PLACED IN CONTACT WITH A MORDANT SOLUTION WHICH ETCHES SAIDEXPOSED SURFACES.